Smoke testing is one of the oldest methods used to discover inflow and infiltration (I&I) issues into our sewer collection systems. Inflow occurs when surface water is able to enter a system through public or private sources. Infiltration occurs when groundwater enters through structural defects in private laterals, sewer pipes, and manholes.


Smoke testing has been an integral part of most Sewer System Evaluation Studies (SSES) as a way to quickly identify sewer cross connections with storm drain lines, structural defects in pipelines and structures, and to also locate illegal private connections like tie-ins to downspouts and surface drains, which is a significant source of inflow to a system during rain events. Smoke testing is also a good first step to quickly pinpoint areas where further, more detailed, investigations should be performed. Smoke testing can test large areas quickly and at a lower overall cost. Problem areas that are found through smoke testing can then be recommended for follow up investigations, such as Closed Circuit Television (CCTV) inspections.


return area


The smoke testing process involves the introduction of a dense and consistent supply of smoke into the pipeline to be tested. The equipment used consists of powerful blowers that are placed on top of manhole rims, liquid smoke or smoke candles, traffic control and/or signage, personnel to walk along the alignment being tested to look for signs of smoke, flags to mark locations where smoke is seen, and a recording device or log sheet to take photos and input information documenting each smoke test.


The first step of any smoke test project is to determine the area to smoke, and then to deliver notices to residences and businesses in the scoped area. The notices explain the process, provide information on the non-hazardous nature of the smoke, what to do if the smoke does enter the building, and instructs owners to fill all plumbing p-traps prior to the date work is scheduled to prevent smoke intrusion into the building. Smoke test crews must notify and coordinate the daily smoke test work area with police and fire so that they don’t confuse the testing with an actual fire or emergency.


After notifications are delivered, and police and fire are on board, the crew mobilizes to the location. Blowers are placed on top of one or more manholes for the sewer segment/s to be smoked. Liquid smoke or smoke candles are used to emit smoke, which is then blown through the smoke test section. With smoke now being blown down the pipe segment, the crew spotters then walk along the test alignment and look for smoke coming out of the ground, sidewalk, or buildings in both the public right of way, and on private property. For test locations that are located inside of private property, advance permission may be required to enter the property to look for smoke.


return area


If smoke is observed, the location is flagged, and then photos and measurements are taken to document the smoke and the nature of the issue.


All results are compiled to indicate the private or public nature of the violation, the cause of the smoke return (downspouts connecting to sewer lateral, possible broken lateral, connection to a private surface drain, cross connection to City storm drain, etc.). This information is provided to the system owner to act on the next important step in the process; repairing or resolving the issue that has potential for I&I. Property owners should be informed of the violation and required to remedy the issue.


Private sources of I&I typically make up the majority of most smoke testing violations. This is because private laterals are not often maintained like the public sewer system is maintained. Most homeowners do not have the tools or knowledge on how to maintain their sewer laterals, and will not spend money on them unless there is a problem.


Several cities in California have found a pro-active way to require property owners to inspect and/or repair their service laterals. Some cities require a passing air test to prove the lateral is leak-tight before the title can be transferred during a sale to a prospective buyer.


National Plant Services chart


Other cities require the homeowner to obtain a CCTV inspection of their lateral when pulling any type of building permit. The inspection video is delivered to the city for review, and the city sends a violation letter requiring the repairs that need to be performed so that a fine is not levied.


These types of regulatory policies greatly assist in the locating and repair of private sewer lateral structural problems. These policies require that a city or sewer district be willing to handle initial policy objections from the community, but it is a necessary step in the reduction of I&I from private sources into our collection systems. I&I greatly increases the size and cost necessary to treat the extra water coming into the wastewater treatment plants. This is a cost not only to the sewer district, but also the ratepayers, so by requiring homeowners to maintain their sewer laterals to prevent I&I, everyone benefits.



Michelle Beason P.E., is with National Plant Services Inc., a Carylon Company.



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